Presently, the common module packaging technologies for LCD are Chip on film (COF), Tape Automated Bonding (TAB) and Chip On Glass (COG). These three technologies described above have become the main streams of the present module packaging technology, and they all use an anisotropic conductive film (ACF) as a conductive bonding medium. ACF is a material with high molecular weight and is formed by dispreading the mixture of the conductive particles and the adhesives on the materials containing the releasing agent. In general, the thickness of the ACF is ranged from 15 to 45 microns, and the different thickness of ACF is used for meeting the requirements of forming the bonding between different objects.
Since there is no way to directly evaluate the quality of the bonding between different components, the management and the development of the bonding area during the processes described above are basically relied on the final evaluative result of the product. Therefore the difficulty of development is increased since it usually takes too much time and money on the reliability experiments for getting an evaluation of the bonding.
The procedures of the current developmental technologies for the module process include the steps of: 1) preparing the standard of the cell and all the relevant component parts of making a trial product, 2) forming the Outer Lead Bonding (OLD), 3) bonding the ACF on the PCB (AOP) or proceeding the solder bonding, 4) assembling the back light module, 5) carrying out an inspection before shipping out the products, 6) carrying out the reliability experiments, such as a temperature-humidity-bias test (THB), a thermal shock test (TST) or a shock test, and 7) analyzing and solving the problems.
And the disadvantages of the current developmental technologies of the module process are described as following:
1) Currently, the developmental stage of the module process is a time-consuming process, and it takes at least two weeks to get an evaluative result. Since the resistance of the bonding area of ACF affects the evaluative result of the reliability experiments of the product, the bonding resistance should reach a standard level to be applied to the product in the module process. Currently, the only way to evaluate the bonding resistance or the quality of the bonding area is to analyze the evaluative result derived from the reliability experiments. In addition, the feasibility of the manufacturing process is determined by the functions of the manufactured product after carrying out the reliability experiments.
2) It is too expensive in the developmental stage of the module process that it must take the products as the test and verify samples.
3) Since there is no direct evidence, it is difficult to define the problems in each procedure by the final evaluative results in the developmental stage of the module process. While functional problems are found after analyzing the evaluative results derived from the reliability experiments, it is usual that much time is spent for redoing the experiment to find out the real problems. Even by doing that only the direction of the problems might be provided by indirect evidences. And the indirect evidences of the problems related to the bonding area are got by comparing the evaluative result with the known data of the other component parts.
4) It is very difficult and time-consuming to evaluate a new material in the developmental stage of the module process. As described above, if the new bonding component parts are introduced, such that a new ACF is used, it is necessary to carry out the new reliability experiments. And without any accidents, this process still takes at least two weeks to get an evaluation. In addition, the materials used for the experiments are very expensive.
5) It is impossible to manage the process by numerical data in the developmental stage of the module process. It is impossible for engineers to evaluate the quality of the bonding area by the exactly numerical data of the bonding resistance in the present module process, and it is often that the products are qualified in the small-scale trail run but some problems are appeared in the large-scale production. Furthermore, to re-evaluate the module process will cause a considerable loss of time and money.
Please refer to FIG. 1 and FIG. 2, which are respectively the schematic view showing the module bonding and the diagram showing the technical design of the outer lead bonding (OLB) of the tape carrier package (TCP) according to the prior art. As shown in FIG. 1, the bonding between the cell 11 and the flexible film 12 is formed by the ACF 14. The bonding between the flexible film 12 and the printed circuit board 15 is formed by the ACF 14. And the driver IC 13 is placed on the flexible film 12. As shown in FIG. 2, the cell 11 has a plurality of pins 111 and the flexible film 12 has a plurality of pins 121, wherein the bonding between the pins 111 and the pins 121 are formed by the ACF 14.
In view of the foresaid descriptions, the bonding between the cell 11 and the flexible film 12 and the bonding between the flexible film 12 and the printed circuit board 15 are formed by the ACF 14 in the present module packing technologies. The ACF 14 is used as a conductive bonding material. Therefore, the quality of the bonding between the cell 11 and the flexible film 12 or the value of the bonding resistance is related to the quality of the module process. The current technologies are unable to do a test directly on the product to examine the manufacturing process of the printed circuit board in real time, so that a test must be carried out on some product samples or a destructive examination must be carried out on the product to test and verify the process. Therefore, it is very inconvenient for the developmental stage of the module process and the analysis of the product currently. The limitations thereof are that it is unable to directly analyze the product and lots of time for the development of product will be lost since that when there is a problem happened on the product it is impossible to examine the influence of the module process thereon in real time. Moreover, in the current examination for the developmental stage of the module process, the dummy printed circuit board used is unable to provide a direct proof of the influence for the module process on the product. Also it costs more time and money but no better verification is obtained.
Since there is no measuring mechanism in the current module bonding technologies, it is very important to provide a mechanism for measuring the bonding resistance in the management of the bonding of the ACF. That is to say that with this design, there is no need to carry out the destructive examinations on products in the reliability experiments, and there is also no need to use the time-consuming and indirect test element group (TEG) samples to test and verify the module process. For that reason, the cost and the time expended and the numbers of experiments be carried out are greatly reduced, and the data can be used for the numerical managements of the mass-market product. In addition, the value of the bonding resistance could be the first item of the checking list.